IVhorseman wrote:Correct me if I'm wrong, but are extremist movements more popular in multiple-party systems than two-party systems?

I'd say so. As of now basically every country in Europe has some extreme-right-wingers in their parliaments. If the American system was reformed the teabaggers might form their own party and get some seats... and if neither other party has a majority they'll be controlling any decision the other parties can't reach an agreement on like Bonn-o-Tron. Which is basically the situation in Sweden right now

Remus: Harry... I'm a werewolf.
Harry: Are you fucking serious?
Remus: Well yes, but I don't see how that applies here.

Usually the other parties make alliances and refuse to ally (I doubt this is the right word, but eh) with the extreme parties, so they're usually kept relatively small or at least relatively powerless, until the voters think 'fuck it this is useless' and join a less extreme (but still pretty bad) right wing party, often allowing this to become a big party in the end. That's what happened here. Democracy at it's best.